The University of Michigan Transgenic Animal Model Core provides transgenic mice and mouse mutants created by gene targeting in embryonic stem (ES) cells. The Core also provides assistance in experimental design and analysis of genetically engineered mice. Demand by investigators for these animals has risen continuously since the core was established in 1988. In the last eighteen months demand has doubled from 40 requests for transgenic mice to 79 and demand for mutant mice increased from four gene "knockouts" to seven. In each of the last three years, five new investigators have used genetically altered mice for the first time. The Transgenic Core needs another micromanipulation workstation to meet this increasing demand and to avoid delays in providing animals. The state-of-the-art instrumentation requested will increase the efficiency of producing animals and add new analytical capabilities needed by users. The new workstation will be used by core personnel and individual users for 1) micromanipulation; 2) determination of embryonic stem cell ploidy by chromosome counting; and 3) analysis of transgene expression by fluorescence. The new workstation will be placed in renovated space, specifically designed for the instrumentation and assigned to the Transgenic Core. Day to day oversight of the workstation will be carried out by the excellent existing core personnel. Dr. Thomas Saunders has 7 years experience as the Transgenic Core manager, including expertise in instrument supervision, user training, and maintenance. An internal advisory committee of experienced users will provide oversight and formalize sharing arrangements. The availability of an up-to-date micromanipulation instrument is important for the research productivity of a growing community of researchers using transgenic and gene targeting approaches to address important biomedical questions.